New ages, morphometric and geochemical data on recent shoshonitic volcanism of the Puna, Central Volcanic Zone of Andes: San Jerónimo and Negro de Chorrillos volcanoes

Shoshonitic volcanic centres are scarce within the back-arc mafic volcanism of Puna Plateau in Central Volcanic Zone Andes. San Jerónimo and Negro de Chorrillos volcanoes two well preserved shoshonitic monogenetic edifices that developed mainly Strombolian activity lava flows, which extended more than 9 4 km from vent, producing a volume DRE (Dense Rock Equivalent) 0.091 0.020 km3, respectively. The new unspiked K–Ar (groundmass) ages (144 ± 3 ka) (51 2 eruptions presented this work both younger those previously published. Petrographic compositional features allow distinguishing between potassic ultrapotassic suites products eruptions. Phlogopite occurrence low glass content characterize suite. Based on crustal thickness part experimental constraint, these magmas last equilibrated at Moho depths around 50 (the highest depth spinel lherzolite stability field) for temperatures 1100–1200 °C. Once crust, K-rich magma underwent minor interaction with trachytic-trachydacitic melt, is evidenced petrographically geochemically, e.g., mismatch mineral assemblages (co-occurrence olivine quartz), disequilibrium crystal textures (dusty zones plagioclase, embayments sanidine), wide range variation glasses. Ultrapotassic (i.e., phlogopite-bearing) lavas same eruption interpreted as pulses but longer mixing time melt resulting rocks an eruptive frame hours or days. singular character could be related to their origin along old terrane boundary. Afterwards, occurs other Puna, major NW-SE fault systems would favour ascent surface.